The invention pertains to a device to analyze the alcohol content of a gas, especially for testing an automobilist's alcoholemia level; more specifically, it pertains to an arrangement of testing circuits which allow it to be ensured that exhaled air is taken under satisfactory conditions of reliability and precision.
It is known that, in order to ensure the reliability of an alcoholemia test, the air sample which is analyzed must come from the deepest part of the lungs: the term "alveolar air" is commonly used to designate the fraction of air which is discharged at the end of a complete exhalation period because it comes from the alveolar passages of the lungs. It is the analysis of the alcohol content of this "alveolar air" which allows the driver's alcoholemia level to be determined with sufficient precision.
Various devices are known which are intended to measure the alcohol content of a gas. For example, U.S. Pat. No. 4,346,584 describes an automatic analyzing device which takes a sample of gas at the end of the exhalation as soon as the pressure decreases in the intake conduit. French Pat. No. 2,449,877 describes a device for taking a breath sample, comprising a pressure sensor which controls the activation of a timing unit which delays the instant at which the measurement is taken. Nonetheless, these known devices do not provide a reliable measurement of the alcohol content of alveolar air under all circumstances.